Transcript for When Grassroots Protest Rallies Have Corporate Sponsors

Tonight, with the final hours ticking down before this year's midterm elections, any local efforts are wrapping up. But in one major city, a battle over a soda tax has led to new questions about whether a growing movement is really what it seems. Here's ABC's David Wright. Reporter: Protest rallies in San Francisco are a dime a dozen. And this one looks real enough. What do we want? Reporter: But take a closer look. You'll see, there's something unusual about this protest. Right there in the fine print. This rally has corporate sponsorship. Let's be frank. This is a front group for coke and Pepsi, right? It's not a front group. We don't hide it. There's no secret about it. That's really not the issue. The main issue is, is this measure right for San Francisco and we don't believe that it is. Reporter: Roger Sal czazar is the spokesman for a group that sounds like it's fighting skyrocketing rents or rampant gentry if I case. Nope. It's dedicated to fighting a proposed tax on sugary soft drinks. You want to make San Francisco more affordable by keeping the price of coke and Pepsi affordable, basically? If the goal is to improve public health, taxing grocery items is not the way to do it. Reporter: Proposition E, often referred to as the soda tax, would tax all sugar sweetened beverages 2 cents an ounce, with the proceeds earma earmarked for programs to educate children towards health area choices in an effort to reduce obesity. Whether or not a beverage tax is the best answer to fight obesity is open to debate. That's not why we're here. We're here to look at that notion astro turf campaigns. Campaigns that look like grassroots efforts, but are bought and paid for by interest groups with deep pockets. Sup supervisor Scott Weiner is the man behind prop E. This is a fake group of the American beverage association. Reporter: This is a coalition of Pepsi, coke. Red bull and sunny D, all the rest. Reporter: Over the past few years, more than 30 other communities have tried to take on sugary beverages and the aba has poured millions into the fight for strike them down. Big soda companies come in with millions and millions of C corporate dollars to spend misinformation. Reporter: But ask the no on E group about it and claim the coalition is huge. There are lots of folks that feel this is the wrong priority for the city of San Francisco. Reporter: We decided to check it out. Our first stop, smoking warehouse barbecue. He tells us the no on E campaigners told him the proceeds of the tax may not actually go to the intended childhood health programs. They told me the money wouldn't go towards education of kids. Reporter: But if it goes toward the education of kids -- I'm for it. Reporter: Next, we went to another restaurant. The manager there pointed out they have a sign in the window supporting prop E. You're saying soft drinks, sugary soft drinks are bad. Yeah. Reporter: They should be taxed? Yeah. Reporter: At Joe's -- doesn't exist anymore. The restaurant's website says it's been closed more than six months. To be fair, the no on E campaign did hand over records of endorsement from all of the bitzs on their list, including Joe's cable car burger joint. We have signed cards for every single one of the businesses. I can't help if they closed after we went and talked to them. Reporter: And we did come across some businesses that do, in fact, oppose the tax. The fizzry is an artisanal soda and candy shop. Its owner, literally the poster boy for the no on E campaign. If it passed, we would lose business for sure. At the base of it, it's a grocery tax and I don't know any shopper that wants that. Reporter: Fair enough. But is that really enough to make the average citizen take to the streets? We've heard accusations that the no on E campaign was actually hiring people to hold signs. Many of whom aren't even San Francisco voters. So, "Nightline" producer Jackie jesco answered this craigslist ad, looking for sign holders. The pay? $13 an hour, right? Reporter: Jackie made sure to tell him she lives 3,000 miles from San Francisco. Well, I actually live in new York. Reporter: No problem, said the campaign guy. It's okay? Okay. Reporter: When she showed up at the no on E rally and tried to talk to some of the protesters -- Is this a paid gig? We're really just doing it for the taxes. Reporter: The campaign quickly shut down her attempts to interview anyone else. Why are you here today? I'm not talking to the press. This isn't a press event. It's a rally. Not talking to anybody? Reporter: But there was one group that was keen to talk to the cameras. This small but vocal pro soda tax group. We're just telling the truth. Reporter: This is Maureen Irwin, leader of choose health sf. The official pro-tax campaign. The pro-tax group is being outfunded 30 to 1. Their mascot, big soda cry baby, hands on monopoly money for votes. More where this came from. Reporter: We reached out to the American beverage association who told us, we oppose taxes or other discriminatory proposals that single out our products. We are completely transparent in our engagement in these debates. If San Francisco passes a soda tax, it sends a very powerful message that big soda can be beaten. Reporter: And if San Francisco doesn't manage to get the necessary two-thirds majority, there's a soda tax on the ballot in Berkeley, too. I'm David Wright for "Nightline" in San Francisco.

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